We're One Step Closer to a Real Invisibility Cloak

When it comes to developing a working invisibility cloak, we may not be at Harry Potter level yet, but today's newest breakthrough is nonetheless impressive.

A team of researchers led by Xingjie Ni—a nano-engineer at Pennsylvania State University—have just unveiled an fascinating invisibility cloak: one that takes the form of a sleek skin of nano-material. While other scientists have recently made headway building bulky and mechanically complex attempts at concealing screens, Ni's is far and away the thinnest and most cloak-like. At 80 nanometers thick, the skin-like material is 1,000 times thinner than a human hair—just twice the width of a flu virus. Their results are published today in the journal Science.

"With our new design we have made it possible to hide a small, 3D object of any arbitrary shape, and have it appear completely flat," says Ni. As well, Ni and his colleagues claim that while testing their invention, they have actually performed the first-ever feat of concealing a random 3D shape in visible light.

Undetectable, Not See-Through

To be clear, Ni's invisibility cloak doesn't exactly wick light around an object, a la Harry Potter. You couldn't see right through a cloaked object. Instead, the cloak cleverly reflects light to create the illusion that a bulky object is entirely flat. So, rather than hiding Harry in a hallway, you could imagine such a cloak one day concealing something like a micro-sized listening device on a wall or mirror.

The mechanics of Ni's invisibility cloak are actually as fascinating they are simple. The skin of the cloak itself is essentially a forest of tiny antennas made of gold bricks, Ni explains, which can be carefully printed onto whatever object needs to be concealed. When light hits one of the antennas—no matter if the antenna is on a sharp corner or just a slight slope—it's always reflected cleanly backwards. That's important, because normally light would bounce off an object in all various directions, creating the visual illusion we see as shape. If you think of light like a barrage of tennis-balls, the antennas make sure the balls always bounce back as if they had just hit a flat wall.

According to Ni, his team's cloak can currently only conceal an object just a few micrometers in size, "although I can see the potential to scale this up to the size range of centimeters or even meters, by using a different fabrication technique," says Ni.

Still, Ni's cloak is not without its limitations, and some are pretty serious.

For one, the nanomaterial skin has to be specifically and painstakingly designed for the exact shape of whatever will be wearing it, he explains. That's because each antenna has a specific reflecting job—each based on the orientation of the concealed device underneath it. Not only does this make designing one of Ni's cloaks an arduous process... it also means a hidden object can't move for the cloak to work.

And right now, while the cloak works even if you're looking at a hidden object from an angle, Ni and his colleagues can only tune it for a very specific wavelength band of light. That means the cloak can work perfectly if you're only looking with red light. But in blue or yellow light, the 'hidden' object may be perfectly visible. For us humans, who use the whole visible light spectrum to see, the cloak wouldn't fool us.

But as the first incarnation of an entirely new technological approach to creating invisibility cloaks, Ni is optimistic that there is plenty of room for improvement. "Keep in mind, this is an entirely new design," says Ni, "and the advantage for future consumer or even military application is that we're starting from a very, very small size." For one, he explains that there's no reason why future cloaks couldn't use an array of various types of antennas—each tuned for a different color of light—to create a visual illusion that could fool the human eye. And if those antennae were tunable, the cloak could adapt to conceal a constantly moving object.

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